Power supply circuit with feedback circuit

1. A power supply circuit, comprising: a pulse width modulation circuit configured for providing a pulse signal; a voltage conversion circuit configured for converting a primary voltage to an output voltage according to the pulse signal; a feedback circuit comprising a sampling branch configured for detecting a current of the voltage conversion circuit and accordingly providing a feedback signal, and a voltage division branch electrically coupled to the sampling branch; and a control circuit electrically coupled to the voltage division branch, configured for disabling the voltage division branch after a predetermined period of time when the output voltage is within a predetermined range.

2. The power supply circuit of claim 1 , wherein when the output voltage exceeds the predetermined range, the pulse width modulation circuit stops providing the pulse signal immediately.

3. The power supply circuit of claim 1 , wherein when the output voltage is less than the predetermined range, the pulse width modulation circuit provides the pulse signal normally.

4. The power supply circuit of claim 1 , wherein the voltage division branch is configured for expanding an anti-overloading ability of the pulse width modulation circuit.

5. The power supply circuit of claim 1 , wherein the sampling branch comprises a sampling resistor electrically coupled between the voltage conversion circuit and the voltage division branch.

6. The power supply circuit of claim 5 , wherein the pulse width modulation circuit comprises a first terminal configured for receiving the feedback signal, and the sampling branch is electrically coupled between the first terminal and the voltage conversion circuit.

7. The power supply circuit of claim 6 , wherein the voltage dividing circuit comprises a voltage dividing resistor and a first transistor, a base electrode of the first transistor is electrically coupled to the control circuit, a collector electrode of the first transistor is electrically coupled to the first terminal of the pulse width modulation via the voltage dividing resistor, and an emitter electrode of the first transistor is grounded.

8. The power supply circuit of claim 1 , further comprising a coupling circuit configured for coupling the output voltage, and correspondingly generating a coupling voltage.

9. The power supply circuit of claim 8 , wherein the coupling circuit is a photoelectric coupler.

10. The power supply circuit of claim 8 , wherein the pulse width modulation circuit further comprises a second terminal receiving the coupling voltage, and the pulse width modulation circuit ceases the pulse signal when the coupling voltage indicates that the output voltage has exceeded the predetermined range.

11. The power supply circuit of claim 8 , wherein the control circuit comprises a first control unit and a delay circuit, the first control unit configured for receiving the coupling voltage and enabling the delay circuit when the coupling voltage indicates that the output voltage is within the predetermined range.

12. The power supply circuit of claim 11 , wherein the control circuit further comprises a second control unit electrically connecting the delay circuit and the detecting circuit, and the second control unit is configured for disabling the voltage division branch under the control of the delay circuit.

13. The power supply circuit of claim 12 , wherein the first control unit comprises a second transistor, a Zener diode, and a pull-down resistor, a base electrode of the second transistor is configured for receiving the coupling voltage, a collector electrode of the second transistor is configured for receiving a power voltage, and an emitter electrode of the transistor is electrically coupled to a negative electrode of the Zener diode, wherein a positive electrode of the Zener diode is electrically coupled to the delay circuit and grounded via the pull-down resistor.

14. The power supply circuit of claim 13 , wherein the delay circuit is an integrator.

15. The power supply circuit of claim 13 , wherein the delay circuit comprises an integrating resistor and an integrating capacitor, an end of the integrating resistor is electrically coupled to the positive terminal of the Zener diode, the other end of the integrating resistor is grounded via the integrating capacitor, and electrically coupled to the second control unit.

16. The power supply circuit of claim 15 , wherein the second control unit comprises a pull-up resistor and a third transistor, a base electrode of the third transistor is electrically coupled to the integrating resistor, a collector electrode is configured for receiving the power voltage via the pull-up resistor, and is electrically coupled to the voltage division branch, and an emitter electrode of the third transistor is grounded.

17. The power supply circuit of claim 1 , wherein the voltage conversion circuit comprises an electronic switch configured for receiving the pulse signal and a transformer having a first coil and a second coil, wherein an end of the first coil is configured for receiving an external voltage and the other end of the first coil is grounded via the electronic switch.

18. The power supply circuit of claim 17 , wherein the voltage conversion circuit further comprises a third coil, a rectifying diode, and a filter capacitor configured for providing an inner power voltage to the pulse width modulation circuit cooperatively.

19. A power supply circuit, comprising: a pulse width modulation circuit configured providing a pulse signal; a voltage conversion circuit configured for generating an output voltage according to the pulse signal; a detecting circuit comprising a sampling branch electrically coupled to the voltage conversion circuit, and a voltage division branch electrically coupled to the sampling branch; and a control circuit electrically coupled to the voltage division branch; wherein when the output voltage is within a predetermined range, the control circuit disables the voltage division branch after a predetermined period of time.